FR4 is a printed circuit board based on glass-reinforced epoxy laminate material. It is the many used material since it is low-cost in contrast with other materials and it can be utilized in many applications.
FR4 Types
You can find various FR4 boards:
Single layer boards, with just copper in the top of the substrate or double layer, with 2 copper layers, one on each side.
With various substrate density. It can be discovered thickness from 0.1 mm up to 3.2 mm. The required thickness will depend on the application it will be used. Typical thinner thicknesses are used in multilayer boards in which the FR4 board is used to distribute signals to other boards, in order to not increase the thickness of the PCB. Higher thicknesses are used when high toughness of the PCB is required since a big PCB is created.
With various copper layer density. Normal copper densities are 17, 35 or 70 um.
Various panel sizes can be bought, the use of one or another will depend on the equipment the manufacturer has and depending on the final size of the requested PCBs. Typical panel sizes are 12x18 inches, 18x24 inches, and 21x29 inches. When you are developing a panel, you have to consider that not all the panel can be used to draw your PCBs. Around 2 inches length and 2 inches width will be used for other purposes, like fiducial holes and other manufacturer tasks and also avoid the panel can bend if work is performed close to the borders.
FR4 Properties
It has a dielectric loss tangent of around 0.017 to 0.025 while, for example, Rogers laminates have typical values of 0.002 and alumina PCBs have values of around 0.0002. The dielectric loss tangent indicates the insertion losses of the material with the frequency. As can be seen, FR4 has greater worths and this is the factor it can be utilized just for low-frequency applications. Due to the fact that at high frequencies, the insertion losses of the lines are greater, in contrast with other, more pricey, alternatives.
Another crucial criterion is the dielectric constant. The normal worth is around 4.6. This worth is somewhat based on the producer and also the thickness of the substrate, but it is a value that normally supplies excellent outcomes when estimations are carried out from it. From this parameter, the relation impedance/thickness of the line can be gotten. When creating RF and digital circuits, this is really beneficial.
It is flame resistant.
It has hardly no water absorption
It has an extremely high dielectric breakdown, higher than 60KV. This suggests a very high voltage is required to change the properties of the material
It keeps its mechanical and electrical homes in different environmental conditions as dry or wet.
Normal temperature levels in which FR4 can work is from -55 to +125 ºC.
There are better FR4 variations that offer other qualities such as lower dielectric values or higher temperature varieties. These boards are not requirements and not all the suppliers will provide them.
FR4 Uses
FR4 is used worldwide for different applications, business, civil, vehicle and even military applications.
It is utilized for DC, digital and low-frequency RF applications.
Practically the overall of DC boards are finished with FR4 because it is the cheapest material, with great efficiency and due to the fact that it is the material all the manufacturers have the possibility to utilize.
FR4 is an excellent option for digital applications, in which, FPGA, microcontrollers, ADCs, DCAs, buses, etc are used.
FR4 boards can be used for low-frequency applications. Approximately 1-2 GHz the properties of this material can be compared with other more expensive choices like Rogers laminates or alumina. From MHz as much as FR4 1 GHz the outcomes will be a little even worse however the distinction in cost can assist to decide for the FR4 choice. From 2 GHz the differences are higher and normally other materials are picked. With FR4 and the matching elements, a broad catalog of RF circuits can be correctly created and made as amplifiers, switches, attenuators, and so on.
The FR4 choice on the PCB order page is the grade designation for the epoxy fiberglass that often forms the PCB core and prepreg layers. In a normal PCB, the core supplies the rigidness and the foundation on which the PCB traces can be 'printed' onto. For double layer boards, an FR4 core separates the top and bottom copper layers whereas, in multilayer PCBs, additional layers of FR4 prepreg are sandwiched between the inner core and the outer copper layers. Typical thinner thicknesses are used in multilayer boards in which the FR4 board is used to distribute signals to other boards, in order to not increase the thickness of the PCB. Higher densities are utilized when high effectiveness of the PCB is needed because a large PCB is created.